1. Technical Field of the Invention
The present invention relates to a resin composition and formed articles obtained therefrom such as films, and furthermore relates to the application of said formed articles and the like to food packaging use. More particularly, the present invention relates to formed articles such as films excellent in the selective gas permeability obtained from a composition comprising polyvinyl alcohol resin (hereinafter abbreviated as "PVA") and specific compounds, and, furthermore, to the application of the aforementioned formed articles to food packaging use.
2. Description of the Prior Art
In the food packaging industry, technological innovation has been achieved in the recent years so remarkably that today's food packaging operations always call for optimal performances to be imparted by each kind of stock material for a given kind of food to be packaged.
Taking the cheese product, which is a kind of fermented foodstuff, for example, wax-coated packaging material has been conventionally used for packaging the natural cheese, whereas plastic materials have also been adopted for the purpose of improving the appearance, increasing the eatable portion and furthermore, for the manufacturing cost reduction's sake. Natural cheese being added with live bacteria to permit the ripening process to progress therein, the bacteria generate carbon dioxide not only during the ripening step, but throughout the later stages of physical distribution. Since such cheese packaged with the ordinary kind of plastic bag swells up with generated carbon dioxide gas, the introduction of such packaging material as will readily transmit carbon dioxide has been awaited. On the other hand, since oxygen has adverse effects such that oxygen accelerates growth of molds on the cheese and also oxidizes the fat content of the cheese, the trade concerned has been desirous of having a packaging material which suppresses transmission of oxygen. For foodstuff other than cheese, e.g. coffee bean, packaging materials that readily permits permeation of carbon dioxide, but considerably restrains permeation of oxygen have been desired.
Although it is desirable that plastic packaging materials intended for use on cheese product, coffee bean, etc. have higher gas transmission rate (hereinafter abbreviated as "GTR") to carbon dioxide and lower GTR to oxygen, such plastic packaging materials that have high GTR to carbon dioxide, almost without any exception, will have high GTR to oxygen.
Therefore, such packaging materials that have low oxygen GTR and have large carbon dioxide GTR to oxygen GTR, namely, high carbon dioxide/oxygen GTR ratio have been wanted.
There is described in the patent gazette of Published Patent Sho 44-2576 a process for producing a PVA film insoluble in cold water and soluble in warm water of 40 Deg. C. or higher, which is obtained by extruding a specific PVA added with a plasticizer, as a separation membrane. It is described in the same gazette that while glycerin is used as the plasticizer, polyethylene glycol can be also used. The film thus obtained, however, is used as the unit package material for detergent and agricultural chemical and as laundry bags. It is not used as a food packaging material for which selective gas permeability is particularly required.
Besides, there is described in the patent gazette of Published Patent Sho 54-15029 (U.S. Pat. No. 4,073,733) a process for producing a web possessing gas permeability by coagulating polyethylene glycol-containing PVA in a liquid phase, although the web thereby obtained is used for separation of urea and vitamin, and is not utilized as a food packaging material, for which selective gas permeability is required, similarly to the case described in Patent Publication Sho 44-2576.